Preparation of graphene oxide/titanium dioxide nanocomposites and its adsorption for AS(III) ions

Arsenic is a naturally occurring element, which is found in both in natural waters and industrial waters. Graphene oxide/Titanium dioxide (GO/TiO2) nanocomposites were prepared by using hydrothermal technique, their structure was observed and their adsorption performance for As(III) in water was evaluated. X-ray diffraction and Raman spectroscopy spectra confirmed the anatase structure of the TiO2 nanoparticles. The adsorption system is mainly depended on the As(III) concentration and follows a pseudo second-order kinetic model. The initial adsorption was rapid and reached equilibrium after 20 min. The overall equilibrium data were well fitted to Langmuir model for the nanocomposites. The adsorption results indicated that the GO/TiO2 nanocomposites can be a good adsorbent material to treat water that contaminated with As(III)

Synthesis of titanium dioxide nanoparticles and their application for simultaneous photocatalytic oxidation of As(III) and sorption of As(V)

In this study, the effectiveness of TiO2 nanoparticles in removing arsenic species from water was enhanced by the photocatalytic oxidation by conversion of As(III) to As(V), which adsorbs more strongly onto the solid phase of adsorbent than As(III). Anatase nanoparticles were synthesized by using sol-gel method and the synthesized nanoparticles were characterized by X-ray diffraction and scanning electron microscopy. Batch adsorption experiment was carried out to analyze As(III) removal capacity of the anatase nanoparticles with and without presence of photocatalytic oxidation reaction. The maximum % of removal of As(III) was found ~56% at pH 6, respectively, when 1 g l-1 anatase nanoparticles were used at the As0 1 ppm without presence of photocatalytic oxidation reaction. In contrast, over 94.7% As(V) have been removed by anatase nanoparticles in a period of 120 min UV-light irradiation. Using photocatalytic oxidation process, As(III) removal from water was improved by UV-irradiation

Enhanced photocatalytic oxidation of As3+ using titania nanoparticles for arsenic removal from water

Excessively high arsenic concentration in natural water and industrial wastewater is now a threatening problem for many countries especially Bangladesh, India, Germany, China and Turkey [1]. Titanium dioxide, a well-known adsorbent material, has been extensively tested for arsenic removal from water. However, arsenate ions (As5+) adsorbs more strongly onto the solid phase of adsorbent than arsenite ions (As3+). Therefore, the effectiveness of TiO2 nanoparticles in removing As3+ species from water have been enhanced by the photocatalytic oxidation in the presence of oxygen in ultraviolet (UV) light. In the present study, the photocatalytic oxidation of As3+ to As5+ is investigated in UV-illuminated TiO2. Batch adsorption experiment was carried out to analyze removal capacity of the TiO2 nanoparticles with and without presence of photocatalytic oxidation reaction and the adsorption isotherms were obtained. Keywords: Arsenic; Photocatalytic oxidation; Adsorption; Titanium dioxide nanoparticles [1] D. Mohan, C.U. Pittman Jr, Arsenic, Journal of Hazardous Materials , vol.142, 2007, 1–53

Comparative study of arsenic removal efficiency from water by adsorption and photocatalytic oxidation with titanium dioxide

Titanium dioxide, a well-known adsorbent material, has been extensively tested in environmental applications, especially in separation technologies. In the present study, TiO2 nanoparticles were synthesized by using sol-gel method for removing arsenic ions from water. Several water/titanium molar ratios were prepared in order to obtain optimum crystalline structure, morphology, and particle size of titanium dioxide nanoparticles. Two types of TiO2 minerals which were rutile and anatese were mainly synthesized at different calcination temperatures. After characterization of synthesized powders by X-ray diffraction and scanning electron microscopy (SEM), batch adsorption experiments were carried out to analyze removal capacity of the titanium nanoparticles. The maximum % of removal of arsenic was found ~77% at pH 3, respectively when 0.1 g rutile type TiO2 nanoparticles were used at the As0 5 ppm. Anatase type of TiO2 nanoparticles had also closer adsorption capacity which was ~63% at pH 6 with the same initial arsenic concentration. In the light of experimental results, titanium dioxide nanoparticles (TiO2) are found as a promising adsorbent material for arsenic removal from water. However, the effectiveness of TiO2 nanoparticles in removing arsenic species from water have been enhanced by the photocatalytic oxidation by conversion of arsenide ions (As3+) to arsenate ions (As5+), which adsorbs more strongly onto the solid phase of adsorbent than arsenite ions (As3+). Therefore, in the present study the photocatalytic oxidation of As3+ to As5+ is investigated in UV-illuminated and solar irradiated TiO2. Residual arsenic concentrations of the solutions treated with titanium dioxide nanoparticles were measured with a Varian, Vista-Pro CCD simultaneous inductively coupled plasma ICP-OES spectrophotometer. The adsorption isotherms, thermodynamic and kinetic parameters with and without presence of photocatalytic oxidation reaction are obtained to analyze arsenic removal capacity of the TiO2 nanoparticles

Fabrication of nano and porous materials & their utilization in the purification of water contaminated with arsenic, copper, and lead

Water pollution mainly caused by arsenic and heavy metal ions is a growing threat to environment and public health. Adsorption is one of the most efficient methods for the removal of the contaminants due to its high efficiency, easy operation and low cost. This thesis aims to develop nano and porous materials, and then implement these into adsorptions of arsenic, lead, and copper in order to investigate an effective water purification system for communities. In this study, specific functional nanomaterials comprising ferric ion loaded red mud, iron oxide/activated carbon, titanium dioxide nanoparticles, and titanium dioxide/activated carbon nanocomposites have been successfully fabricated. The obtained nanomaterials are characterized by using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectrometer. The arsenic removal efficiency of ferric ion loaded red mud considering effect of pH, initial arsenic concentration, and contact time is evaluated and the higher adsorption capacities found 11.640 mg/g for As(V) at pH 7.0 and 5.254 mg/g for As(III) at pH 2.0. The presence of ferric ion in the system increased the uptakes of arsenic species from water; therefore, the following study is focused on utilization of iron oxide nanoparticles deposited uniformly on activated carbon support with high loadings by microwave hydrothermal treatment. Maximum adsorption capacity is 27.78 mg/g for As(V) and for a loading of 0.75 g/L, 99.90% uptake is reached within 5 minutes. On the other hand, the beneficial adsorptive eliminations of Pb(II), Cu(II), and As(III) from water are also demonstrated using anatase nanoadsorbent produced by sol-gel method. The maximum experimental adsorption uptakes were 31.25 mg/g for Pb(II), 23.74 mg/g for Cu(II), and 16.98 mg/g for As(III), respectively. XPS analyses revealed that the surface oxygen-containing functional groups including hydroxyl groups were involved in the adsorption process. In order to prevent release of the nanoparticles to the environment, activated carbon was used as a support material for TiO2 nanoparticles. It was observed that As(III) uptake capacity of the nanocomposite was improved approximately 2.7 times as compare to the bare TiO2 nanoparticles. Finally, the effectiveness of titanium dioxide nanoparticles in removing arsenic species from water was enhanced by the photocatalytic oxidation experiments converting As(III) to As(V). The maximum adsorption capacities were found 12.13 mg/g for As(III) in the absence of UV-A illumination, 41.38 mg/g for As(V), and 36.55 mg/g for As(III) in the presence of UV-A illumination. Overall, anatase nanoadsorbent are able to reduce Pb(II) and Cu(II) concentrations below the MCL requirements for drinking water. The enhanced As(III) removal are observed under UV-A illumination by using TiO2 nanoparticles and they are able to reduce As(III) concentrations below the MCL requirements for drinking water up to moderate initial concentrations. Additionally, 10-AC/TiO2 nanocomposite, having a considerable As(III) uptake capacity, can be also potentially used in arsenic removal

Combustion characteristics of Turkish hazelnut shell biomass, lignite coal and their respective blends via thermogravimetric analysis

Thermal behavior and combustion kinetic of coal, hazelnut shell, and coal/hazelnut shell blends at the proper ratio were investigated with thermogravimetric analysis (TG). Four mass ratios (20, 30, 40, 50 mass %) of coal/biomass blends were prepared and oxidized under dynamic conditions from temperature 298 to 1173 K at different heating rates. TG analysis indicated that the combustion of blended samples divided into two stages namely devolatilization and char oxidation combined with coal combustion step. The influence of biomass blends on thermal and kinetic behavior of coal was studied under non-isothermal conditions. It was found that the thermal degradation temperature of coal was higher than that of blended samples due to the molecular structure strength. Ozawa–Flynn–Wall model was applied to deal with non-isothermal TG data for the evaluation of the activation energy corresponding to the combustions of coal, hazelnut shell, and coal/hazelnut shell blends. The average activation energy changed in the range of 90.9–215.3 kJ mol-1, respectively, depending on blending ratio

Synthesis of mesoporous MCM-41 materials with low power microwave heating

Crystalline, high surface area, hexagonal mesoporous MCM-41 having uniform pore sizes and good thermal stability was successfully synthesized at 90-120oC in 30 minutes using low power microwave irradiation. This appears to be the first comprehensive and quantitative investigation of the comparatively rapid synthesis of mesoporous MCM-41 using low power microwave heating of 80W (90oC) and 120W (120oC). The influence of reaction temperature and the duration of heating were carefully investigated and the calcined MCM-41 materials were characterized by XRD, SEM, TEM, nitrogen adsorption, TGA and FTIR. The mesoporous MCM-41 product synthesized in 30 minutes at 120W and calcined at 550oC had a very high surface area of 1438 m2/g and was highly ordered, contained uniform pores with diameters in the range of 3.5-4.5 nm. The wall thickness of the materials highly depended on the power of the microwave energy used during the synthesis. Synthesis of the mesoporous MCM-41 products at 120oC resulted with a structure having thinner walls. The mesoporous MCM-41 materials synthesized in the present work had good thermal stability

Synthesis and characterization of iron-impregnated pre-oxidized activated carbon prepared by microwave radiation for As(V) removal from water

One of the most efficient ways to treat water is probably by adsorption and catalytic oxidation. Surely, for such a process to be economical, the catalyst and the adsorber should have a high catalytic activity and adsorption capacity, and be inexpensive. One of these materials is iron oxide, which is studied and used in areas like catalysis and environmental applications. It is known that synthesizing iron oxides in nano size enhances the catalytic activity. Pre-oxidized activated carbons impregnated with iron-based nanoparticles are prepared in a single step under hydrothermal conditions with microwave radiation. The hydrothermal treatment provides an important advantage by forming fine particles that can easily impregnate deep in to the porous support by the help of water. Their efficiency for the removal of As(V) from water was compared with the pure pre-oxidized activated carbon and iron oxide nanoparticles impregnated without microwave radiation. The synthesized nanomaterials with different iron oxide loadings were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analyzer. Iron loadings were calculated using flame atomic absorbance. Microwave radiation provided much faster iron impregnation on the active carbon surface. At the first stage of microwave radiation iron oxide impregnation is low but after 6 minutes, iron oxide nanoparticles of 100 nm size started to cover the surface homogeneously. Further treatment with microwave increased the size of particles and the amount of surface coverage. Additionally, with microwave hydrothermal treatment, relatively higher iron oxide loadings were achieved within 10 minutes. From the XRD characterization it was seen that at the first stage of radiation, iron deposited in the form of -FeOOH, but after the first stage the structure became Fe2O3. While radiation increased the surface area of the material during the first stages, at the last stage the surface area did not increase because of complete surface coverage. Laboratory experiments were carried out to analyze removal capacities of the adsorbents, and also to achieve adsorption isotherms and kinetic parameters. The adsorption was strongly dependent on pH, adsorbent dose and As(V) concentration. Percentage removal of As(V) increased with the decrease in pH value of solution and in order to obtain an effective arsenate removal, the adsorption experiments would require pH values between 3 and 5 for the adsorbent materials. According to kinetic sorption data, for all adsorbent materials, higher regression coefficients (R2) were obtained after the application of pseudo-second order to the experimental data of As(V)’s initial concentrations. The results indicated that iron-impregnated pre-oxidized activated carbon is one of the appropriate adsorbents which can be used for water contaminated with arsenic

Template synthesis of boron nitride nanotubes over iron impregnated mesoporous silica MCM-41 by chemical vapor deposition technique

BN nanotubes were successfully grown over iron impregnated MCM-41 at a relatively low temperature of 750oC for 1 hour by CVD technique. BN nanotubes were obtained after the purification procedure including HCl and HNO3 treatments to remove impurities. SEM image showed the formation of nano-fibrous network BN structures in the diameter range of 20 nm to 40 nm. Both XRD and FTIR characterization results supported the formation of h-BN and c-BN nanostructures. Oxidative TGA results indicated that the synthesized BN nanostructures were thermally stable at temperatures higher than 550oC. Hydrogen storage measurements via IGA showed that BNNTs could adsorb 0.85 wt% hydrogen which was two times larger than for commercial CNTs

Biogasification and combustion reactions of Turkish lignites: adsorption behavior and biogasification of Soma lignite and co-combustion of Beypazari lignite with biomass

In this study, our primary objective is to understand CBM capacity of the Soma coal basin. For this reason, porosity of the coal samples must be determined. Usually, surface area and the porosity of the materials can be calculated through the N2 physical sorption experiment, in this method entire relative pressure range (10-8 to 1) can be analyzed without using high pressure equipments. However, for microporous materials like carbon materials and zeolites physical sorption occurs at very low relative pressure ranges (10-8 to 10-3) and experiments that are conducted with N2 are less reliable due to the low diffusion rate and adsorption equilibrium in the pores between 0,5 to 1 nm at 77 K. It is also known that specifically for carbon materials experiments that are conducted at low temperatures such as N2 sorption causes pore shrinkage that leads to the low sorption equilibrium